We just used a cheap rucksac from Millets - lots of pockets so easy to organise, can be on you or the pushchair, not offensive to DH, and has a life afterwards. Used a big terry nappy square as a changing mat.

How about messenger style ones from Argos? I bought a black tigger one (lots of school kids have them too), water resistant, easily fits everything and changing mat, only 12.99 each. Also got a hot pink ripcurl one, not quite so stylish as my yummy mummy one (what a waste of money that was) and brill as swimming/gym bag.